Heal is the amount healed when proc'd. [input]
Times is the number of ticks that occurred between the last and current proc. (0 to 3) [input]
Total starts with a value of 0 and carries over to the next proc.
HoT is the amount healed over time.
Tick is the amount healed per tick.

Proc # is the order in which each proc takes place.
The total has a before and an after.
Before is the amount carried over from the previous proc.
After is calculated based on how many ticks between the last proc plus the amount healed that activated the current proc #.
If times equals 0, total (after) can be calculated as simple as "total (before) + heal".

The following examples have been rounded to the nearest tenth to make it easier to read.

If you happen to proc over and over and over again, the amount of healing lost if 1 tick were to happen grows bigger and bigger.
The way to calculate this is basically backwards from the proc calculations.

Amount = #[input]
Total HoT = Amount*3
Total Heal = Amount/0.33

An easy way to calculate the amount you need to heal to get it back up:
Healing Lost = Total Heal*(Ticks/3)